High internal phase emulsions stabilized by walnut protein amyloid-like aggregates and their application in food 3D printing

This study comparatively investigated the rheological properties of high internal phase emulsions (HIPEs) stabilized by walnut protein isolate (WPI) and its amyloid-like aggregate form (WPIA) in detail. WPIA was generated through combined acidic and thermal treatment. Transmission electron microscopy revealed a long rod-like fibrillar structure in WPIA. At pH 3.0, WPI effectively stabilized HIPEs by functioning as a soluble protein emulsifier, while WPIA stabilized Pickering-type HIPEs (HIPPEs) by functioning as solid particles. HIPEs stabilized by WPI at pH 3.0 displayed a slightly higher storage modulus but lower yield strain/stress and a higher loss factor compared to those stabilized by WPIA. Notably, WPIA-stabilized HIPEs showed more pronounced weak strain overshoot behavior. At pH 7.0, WPIA-stabilized HIPEs exhibited a lower storage modulus but higher yield strain compared to pH 3.0 preparations. WPI failed to stabilize HIPEs at pH 7.0 due to its poor solubility. HIPEs stabilized by WPIA at pH 3.0 exhibited good long-term storage stability and had relative resistance to heat treatment and high ionic strength. Furthermore, both WPI- and WPIA-stabilized HIPEs at pH 3.0 exhibited good 3D printability. These findings provide valuable insights into the effect of different folding states of the same protein (WPI and WPIA) on the properties of the resulting HIPEs and offer a novel strategy for expanding the use of walnut proteins in the food industry.